Accelerated apoptosis characterizes cyclosporine-associated interstitial fibrosis

Recently we developed a model of cyclosporine nephropathy in rats characterized by tubulointerstitial (TI) injury, macrophage infiltration, and progressive interstitial fibrosis [1, 2]. To determine if the TI injury accompanying cyclosporine A (CsA) nephropathy was associated with accelerated apoptosis and ischemia, we treated rats for five weeks with CsA with or without losartan (to block angiotensin II type 1 receptor), or hydralazine/furosemide (H/F) (protocol #1). In protocol #2, rats received CsA with or without L-NAME (to block nitric oxide) or L-arginine (to provide a precursor to nitric oxide formation). Cyclosporine A treated rats had increased apoptosis of tubular and interstitial cells documented by PAS, propidium iodide staining, TUNEL assay, and electron microscopy compared to vehicle treated controls. Macrophages containing apoptotic cells could be confirmed by TUNEL/ED-1 doublestaining and colocalized in areas of TI injury. Animals treated with CsA + losartan had a statistically significant decrease in apoptosis (TUNEL + cells/mm2) when compared to CsA treated animals (6.0 vs. 19.9, P < or = 0.0001). The decrease in apoptosis in the CsA + H/F group was not statistically significant. Animals treated with CsA + L-NAME had a statistically significant increase in apoptosis compared to the CsA treated animals (12.3 vs. 6.4, P = 0.001). L-arginine administration with CsA resulted in a decrease in tubulointerstitial apoptosis versus CsA treated animals, however, this did not reach statistical significance. The addition of L-arginine did result in a significant reduction in interstitial fibrosis (P < 0.0001). Regression analysis revealed a significant correlation between apoptosis and interstitial fibrosis in both protocols. (CsA vs. CsA + losartan r = 0.63, P < 0.0001; CsA vs. CsA + L-NAME r = 0.83, P < 0.0001). We conclude that CsA nephropathy is associated with a marked increase in apoptosis of tubular and interstitial cells. Cyclosporine A induced apoptosis is partially mediated by angiotensin II and nitric oxide inhibition, suggesting a role for renal ischemia in this process, and CsA induced apoptosis correlates with interstitial fibrosis.